Motor vehicle braking apparatus



June 2, 1970 B. E. STEVENSON ETAL 3,515,438

MOTOR VEHICLE BRAKING APPARATUS Original Filed Nov. 14, 1966 4Sheets-Sheet 1 J1me 1970 B. E. STEVENSON EF L 3,515,438

MOTOR VEHICLE BRAKING APPARATUS Original Filed Nov. 14. 1 966 4Sheets-Sheet 2 INVENTORS. fizz/5 WWI/WM BY 72/0/1445 F fimrz/ AffJF/l EIH June 2, 1970 STEVENSQN ETAL 3,515,438

MOTOR VEHICLE BRAKING APPARATUS Original Filed NOV. 14 1966 4Sheets-Sheet 5 B. E. STEVENSON Er AL MOTOR VEHICLE BRAKIN Original FiledNov. 14 1966 xii June 2, 1970 a M /flf W .jllm 4 M M W h W w w 5 firm MWW M w; W w WM 32 W M WW Z 65; 2; 5M w w i w? fwf wfzfa 441i 4 5 5 M w W5 6 f? h m A y W M M f 4 W m 6 w Z w 1 w r W1. /:1 ,WI 1 i 1 M w W 4 5 v2 HM 1m e mm mm M m United States Patent 3,515,438 MOTOR VEHICLE BRAKINGAPPARATUS Billy E. Stevenson, Huntington Beach, and Thomas R.

Rumsey, Inglewood, Calif, assignors, by mesne assignments, to RoyalIndustries, Inc-, Pasadena, Calif., a corporation of Delaware Originalapplication Nov. 14, 1966, Ser. No. 593,818.

Divided and this application Sept. 18, 1968, Ser.

Int. Cl. B60t 13/38 U.S. Cl. 303-9 2 Claims ABSTRACT OF THE DISCLOSURE Avehicle braking system for operating a combined service/emergency andbooster unit. The system includes an emergency valve for controlling theamount of fluid pressure applied to the emergency brake for operationindependent of the service brake and independent of the booster brake.The booster brake may be controlled by a conventional control systemthrough a quick release valve or through the combination of adifferential pressure check valve and parking valve arrangement foradditional protection.

This application is a divisional application based on copendingapplication bearing Ser. No. 593,818 filed on Nov. 14, 1966 and assignedto the same assignee as the present application; and now Pat. No.3.4l7,671 granted on Dec. 24, 1968.

This invention relates to motor vehicle braking apparatus and moreparticularly to an improved service brake and combinationservice/emergency brake assembly for use with trucks or tractors andtractor-trailer combinations and the like, allowing the vehicle operatorto continuously control the amount of braking of the vehicle.

There are presently available power actuated braking systemscharacterized as fail safe braking systems utilizing pressurized fluidor air to control the vehicle service brakes for both emergencyoperation and for parking purposes. These power actuated booster brakesare employed to complement the usual service braking units on motorvehicles such as trucks or tractors or tractortrailer combinations.These booster units are mounted in a piggyback fashion with theassociated service brakes and are employed for emergency and parkingpurposes. These auxiliary booster brakes are fluid operated devices thatare normally maintained in a de actuated condition in response to fluidunder pressure and are constructed and designed to be responsive to thecomplete loss of the fluid under pressure or the loss of pressure belowa preselected pressure for actuating the braking unit; failing safe. Itshould also be appreciated that both the present day standard servicebrakes and booster brakes are constructed and defined to be either in afully actuated condition or a fully deactuated condition. The standardservice brake is operated by the application thereto of a fluid underpressure while the booster brake is automatically responsive foremergency operation due to the failure of the fluid under pressure.Alternatively, when the booster brake is employed for parking purposes,the operator normally exhausts the fluid under pressure from the boosterbrake to actuate the booster brake and thereby the braking unit. Atypical service brake and service booster brake combination is disclosedin the co-pending application bearing Ser. No. 467,189 filed on June 18,1965 entitled Fluid Operated Braking System, now Pat. No. 3,285,672 andassigned to the same assignee as the present application.

Experience with the braking apparatus of the type under considerationhas proven that a booster brake con- Patented June 2, 1970 "ice structedand defined in terms of a spring brake is a superior arrangement to allother methods and braking apparatus for positively parking a vehicle.All presently known spring booster brakes rely Wholly upon the forceexerted by a compressed compression spring to effect the brak ng actionunder the control of the operator for parking purposes or toautomatically effect an emergency stop. The spring booster brake hasbeen found to securely brake a motor vehicle such as a truck or trucktrailer combination in a stationary stop. The very use of a compressionspring in a booster brake requires certain characteristics when it isdesired to employ it for braking and emergency stopping purposes thatrender it ineffective for allowing the operator to completely controlthe brakmg action.

At the present time there is a need for an auxiliary braking device toallow the motor vehicle operator to control the braking action in thesame fashion the conventional braking system for a motor vehicle iscontrolled by the operator under emergency conditions. These emergencyconditions should be distinguished from the emer gency conditionsrendering the spring booster brake onerative mentioned hereinabovewherein the brake is fully actuated. The type of emergency braking thatis desired is related to the condition of the road whereby the operatorrequires certain control over the speed of his vehicle to avoid anobject on the road, or obstruction in the road or the like, requiringbraking in increments depending on operator judgment. Present daycompression springs employed in booster brakes are constructed anddefined to be either in a fully compressed condition whereby the brakeunit is deactuated or in a fully released position for actuating thebrake unit. Such conventional springs therefore are also designed to becompressed with a maximum air pressure of 90 pounds per square inch. Inaddition, due to the limited amount of space for mounting the servicebrake and the booster brake, the spring for the booster brake must be ofsuch size as to have a minimum length to facilitate its installation onthe vehicle. To control the compression spring of a booster brake forthe desired emergency application mentioned hereinabove by controllingthe amount of fluid pressure applied to the booster brake has been foundnot to be practhe compression spring will create a drag on theconventional brake resulting in excessive wear of the brake blocks andbrake drums.

The present invention provides an improved service/ emergency brakeassembly that may be employed with the conventional braking unit whichallows for modulated control of the service brake assembly for emergencypurposes and yet affords the conventional service brake operation. Inaddition, the conventional service/emergency brake is of a constructionthat allows it to be used with present day commercially availablebooster brakes and to be arranged and operated therewith in the usualpiggyback fashion. The improved braking apparatus of the presentinvention may be considered a double safe unit to maintain the effectivepositive parking feature of the spring booster brakes and also furnish asafe modulated emergency application of the vehicle brakes with aneifectiveness closely approximating the application of the normalservice brakes. The construction and design of the improved serviceemergency brake of the present invention meets the general requirementswith regard to space for mounting this type brake unit since it isapproximately one-half inch longer than present brakes 3 of this typethat do not incorporate the emergency braking feature.

The emergency braking feature embodied in the present braking apparatusresults through the use of a standard diaphragm and therefore eliminatesthe need for any special diaphragms having built-in centers as employedin certain other prior art types of service/emergency braking units. Therelatively simple construction of the service/emergency braking unitrenders it relatively inexpensively with respect to similar competitiveunits. The internal construction of the brake unit allows the use of thestandard diaphragms whereby the braking unit may be readily assembled bymeans of a single clamp further allowing for the ease of assembly anddisassembly of the brake.

From a structional standpoint the conventional service and emergencybraking assembly comprises a housing adapted to be secured adjacent thebraking unit and enclosing the simuilarly constructed and definedflexible diaphragms supported across the housing. The diaphragms aresupported and spaced by means of a spacer ring having preselecteddimensions with respect to the effectiveness of the braking actionalforded by both of the diaphragms. In this fashion, a pair of fluidchambers are defined whereby one chamber is defined between the faces ofthe diaphragms while the second chamber is defined between the end ofthe housing and the adjacent diaphragm. The internal diaphragm can beconsidered the conventional service diaphragm as in the prior artbraking apparatus, while the remaining diaphragm may function as anemergency diaphragm. The diaphragms in their normal operatingrelationship are held adjacent an end of the housing by means of a brakeactuating rod resiliently held against the service diaphragm therebyplacing the center portions of the two diaphragms in a side-by-siderelationship. The opposite end of the brake actuating rod extendsaxially through the opposite end of the housing for operating the brakeunit. The spacer ring for supporting and mounting the pair of diaphragmsincludes means for admitting fluid under pressure between the diaphragmsfor actuating the brake actuating rod for the usual service brakeoperation. In addition, the housing is defined for admitting pressurizedfluid between a surface of the emergency diaphragm and the adjacent endof the housing for controllably actuating the emergency diaphragm andthereby the brake actuating rod in increments under the control of thevehicle operator for controllably operating the braking unit.

From the standpoint of the vehicle braking system, the fluid controlsystem for operating the service/emergency unit along with the boosterunit includes means for modulating the flow of fluid under pressure forapplication to the emergency diaphragm of the combinationservice/emergency braking unit. For this purpose the fluid controlsystem includes an emergency tank connected with the conventional tankmeans and compression unit presently employed on such motor vehicleswhereby the emergency tank is isolated for emergency use only. The fluidcontrol system includes a modulated emergency valve readily accessibleto the vehicle operator for controlling the amount of the fluid pressureapplied to the emergency brake for operation independent of the servicebrake and independent of the operation of the spring booster brake. Thebooster brake employed may be controlled by means of a conventionalcontrol system through the usual quick release valve or through thecombination of the differential pressure check valve and parking valvearrangement for additional protection. These and other features of thepresent invention will be more fully appreciated when considered in thelight FIG. 2 is an elevational view of the brake unit of Fig.1;

FIG. 3 is a detached, front elevational view of the spacer ring for theservice/emergency brake unit of FIG. 1;

FIG. 4 is a sectional view taken along the line 44 in FIG. 3;

FIG. 5 is a partial top plan view of the ring as illustrated in FIG. 3;

FIG. 6 is an enlarged, detailed view of the grooves in the diaphragmsealing portion of the ring in FIG. 3;

- FIG. 7 is a partial, detached view of the relationship of a diaphragmfor service/emergency unit of FIG. 1 and the sealing portion of themounting ring,

FIG. 8 is a partial, cross-sectional view of the sealing ring anddiaphragms for the service/emergency unit of FIG. 1 showing theirassembled relationship;

FIG. 9 is a schematic view of the fluid control system for a combinationservice/emergency unit and a booster unit embodying the invention; and

FIG. 10 is a modified fluid control system for use with the invention.

Now referring to the drawings and to FIG. 1 in particular, thecombination service/emergency unit embodying the invention will bedescribed. FIG. 1 illustrates in cross section a brake apparatus 10 thatcomprises a service/emergency braking unit 11 connected with a boosterunit 12 in the conventional piggyback fashion. It will be appreciated bythose skilled in the art that the brake apparatus 10 illustrated in FIG.1 is typical of the brake apparatus applied to a pair of wheels of atruck or tractor, or tractor hauled trailer and that at least a pair ofthe wheels will carry the braking apparatus 10'. For this purpose, thebraking apparatus 10 is provided with a braking apparatus 10 isillustrated in FIG. 1 under the condition where the fluid under pressureis fully applied to the booster unit 12 as it is arranged in normaloperation for parking purposes and emergency operation.

The construction of the booster unit 12 is of conventional constructionand such booster units are commercially available from the OverlandAnchorlok Division of Royal Industries, Inc. of Culver City, Calif.Briefly the booster unit 12 comprises a housing 13B including a boosterdiaphragm 14 mounted across the housing to define a pair of chambers onopposite sides thereof. A chamber 15 defined on the right side of thebooster dia phragm 14, as illustrated in FIG. 1, defines a chamber forcaging a conventional booster compression spring 16 therein. Thecompression spring 16 is mounted against a floating bearing plate 17mounted adjacent the right hand side of the diaphragm 14 and the outerend of the housing 13B. In the illustrated caged or fully compressedcondition of the spring 16, the spring is maintained between the bearingplate 17 and the adjacent wall 13 of the housing 13B. It will also benoted that the compression spring 16 positions and holds the floatingbearing plate 17 against the face of the booster diaphragm 14. Theopposite sides of the booster diaphragm 14 mounts a push rod 18 having apush plates 20 and 21 mounted to opposite ends thereof. The push rod 18is maintained within the chamber 22 which may be considered as the fluidor air chamber for the booster unit 12. The chamber 22 is defined bymeans of the fluid exposed surface of the diaphragm 14 furtheridentified by the reference character 14*, the opposite face of thechamber being defined by the housing 13B proper and more particularlythe wall identified by the reference numeral 13 The push rod 18 isslidably mounted through the wall 13 of the housing in a fluid tightfashion to maintain the chamber 22 properly pressurized. For thispurpose an O ring 23 is mounted within the wall 13*. A spring 24 ismounted within the air chamber 22 between the push rod plate 20 and thewall 13 of the housing 13B to maintain a minimum amount of pressure onthe booster diaphragm 14 and thereby the compression spring 16.

It should be recognized that with the fluid chamber 22 fully pressurizedthat the push rod 18 will be arranged as illustrated in FIG. 1. Upon thecomplete failure of the fluid pressure to the fluidchamber 22 or whenthe pressure within the chamber falls below a predetermined pressure thecompression spring 16 will be allowed to expand against the boosterdiaphragm 14 for moving the diaphragm to the left thereby operating thepush rod 18. The push rod 18, in turn, will be effective for operatingthe brake operating rod 13 through the service/emergency unit 11 in theusual fashion and thereby the braking unit. The above-described boosterunit 12 is of conventional construction and the booster unit, per se,does not form a portion of the present invention.

The booster unit 12 is arranged in the conventional piggyback fashionwith the service/emergency unit 11 whereby the push rod plate 21 for thepush rod 18 is mounted within the service/emergency unit 11 proper toallow for the piggybac or tandem operation of the service/emergency unit11 and the booster unit 12.

Now referring to the service/emergency braking unit 11 in particular, itwill be seen that it is of the same general configuration andconstruction as present day service units that are not provided with thecontrolled emergency feature. In the disclosed embodiment theservice/emergency unit 11 comprises a housing 30 having the usual brakeactuating rod 13 axially mounted therein and extending between theservice diaphragm 33 and the left end of the housing 30, as illustratedin FIG. 1. The brake actuating rod 13 axially extends through theinterior of the housing 30 and has an enlarged push rod plate 31 securedto its interior end. The push rod plate 31 is resiliently mounted withthe face 31 adjacent the inner end of the service diaphragm 33 by meansof a spring 32. The spring 32 is seated between the opposite face of thepush rod-plate 31 and the inner wall 30 of the housing 30. The diaphragm33 has been specified as the service diaphragm of the service/emergencybraking unit 11. A spacing and mounting ring 34 mounts the servicediaphragm 33 on one side thereof, and an emergency diaphragm 35 on theopposite side thereof. The emergency diaphragm 35 is mounted to the ring34 in the same fashion as the service diaphragm 33 to extend across thehousing 30 to thereby define a pair of fluid chambers on opposite sidesof the emregency diaphragm 35, as will be described more fullyhereinafter.

An important feature of the present invention is the fact that theservice/emergency unit 11 is constructed and defined whereby standardcommercially available diaphragms may be employed for both the serviceand emergency features of the unit 11. These diaphragms are consideredconventional in the sense that their construction is similar to presentday service diaphragms employed in the type of braking units underconsideration and, in fact, are similar in construction to the boosterdiaphragm 14 described hereinabove.

The fluid chamber defined between the diaphragms 33 and 35 identified bythe reference letter S is the fluid chamber for operating the servicediaphragm 33. The fluid chamber defined on the opposite side of theemergency diaphragm 35 is considered the emergency chamber E. Theemergency diaphragm 35 is further illustrated with its midsectionabuting the push rod plate 21 of the booster unit 12. The unit 11 isfurther arranged so that the midsections of diaphragms 33 and 35 areplaced in a side-by-side relationship or abuting one another, asillustrated in FIG. 1. It will also be appreciated that theservice/emergency unit 11 is actuated through the independentapplication of fluid under pressure to the service fluid chamber S andthe emergency fluid chamber E for moving the brake activating rod 13.The ring 34 mounting the diaphragms 33 and '35 is secured to the housing30 by means of a single clamping element 36.

Another important feature of the present invention is the constructionof the spacing and mounting ring 34 for spacing and mounting the servicediaphragm 33 and the emergency diaphragm 35 in the correct relaitonshipto provide effective braking action. The width of the ring 34 is definedto allow standard diaphragms to be employed for both service andemergency purposes. This should be contrasted with prior artservice/emergency braking devices wherein at least a single diaphragmmust be specifically constructed with a built-up center section forrendering it effective to produce the desired brake actuation.

The ring 34, as illustrated in FIGS. 3-5, is provided with a fiuid entryport 34 extending therethrough. The fluid entry port 34 is defined toaccept a conventional coupling device for conveying fluid, such as airunder pressure, to the port 34 and thereby to the service fluid chamberS, as illustrated in FIG. 2. The coupling device extends through asuitable aperture in the clamp 36 to which a fluid conduit is connectedto the fluid control system to be described immediately hereinatfer. Oneof the limiting factors with respect to the width of the mounting ring36 is the size of the fluid port 34 required for proper operation. Thisis considered in accordance with the present invention and the minimumwidth of the ring 36 is on the order of 0.365 inch. It will also beappreciated that the effectiveness of the emergency diaphragm 35 dependsupon its spacing from the service diaphragm 33 and its effectivenessdecreases with the increase in the spacing. To allow conventionaldiaphragms to be employed and to maintain-the desired effectiveness forthe emergency diaphragm 35, it has been found that the maximum spacingbetween the two diaphragms 33 and 35 should be on the order of 0.500inches. Specificcally, then the width of the ring 34 may fall Within0.365 inches and 0.500 inches and it has been further determined that aring width of 0.465 inches is preferable.

In addition to the definition of the width of the ring 34 within theabove-described limits, the ring per se has important features withregard to the sealing action it affords with respect to the diaphragms33 and 35. The ring 34, as best viewed in FIGS. 4, 6 and 7, is providedwith a sealing feature defined by the undercut portions 34 adjacent theouter periphery of the ring 34. The ring 34 is undercut at the portions34 on the opposite faces of the ring for defining sealing flanges 34 onthe same faces. In addition to the flanges 34 the undercut portion '34is grooved by means of grooves 34, as best illustrated in the enlargedsectional view of FIG. 6.

Thruogh the provision of the sealing flange 34 an outer sealing area iscreated for sealing the diaphragms 33 and 35 within the housing 30 ofthe service/emergency unit 11. In addition, the definition of theflanges 34 on the rings 34 avoids the usual bolging of the diaphragms atthe point of mounting as in conventional constructions and provide animproved seal leading to the elimination of leakers. The construction ofthe rings in this fashion also allows both the service and emergencydiaphragms 33 and 35 to be mounted and assembled together and therebylocked by a single clamping element 36 to the housing proper with aminimum eifort and expense.

It should also be noted that the continued operation of the diaphragms33 and 35 causes the adjacent faces identified as 33R and 35R of thediaphragms 33 and 35 to continuously move or r-ub against one anotherand therefore present a wear area. It has been found that the use ofconventional diaphragms are satisfactory for up to 25,000 cycles, andthat the life of these diaphragms can be improved by the application ofa non-friction agent to the designated surfaces of the diaphragms 33 and35 leading to the reduction of wear between the diaphragms. Thisnon-friction agent can be applied over the entire wear surfaces 33R and35R of diaphragms 33 and 35. Although it may be convenient to apply thenon-friction agent over the entire surfaces 33R and 35R, the agent needonly be applied to these surfaces at preselected areas on opposite sidesof the midsections of the diaphragms.

Now referring to FIG. 9, a fluid control system allowing dependableoperation of the service/emergency units 11 and the booster unit 12 willbe described. It should be appreciated that the housings for the brakingapparatus includes the housing 13B for the booster unit 12 and thehousing 30 for the service/emergency units 11 mounted in the piggybacfashion. The pressurized fluid, which may be air under pressure, isadmitted into the fluid chamber 22 for the booster unit 12 by means ofthe fluid port 40 provided in the housing 13B. In the same fashion, thefluid under pressure to be applied to the fluid chamber E is applied bymeans of the fluid port 41 defined in the housing 30. The fluid isadmitted into the chamber S as previously described by means of thefluid port 34 The fluid control system illustrated in FIG. 9 is arrangedfor a pair of braking units 10 associated with a pair of wheels to bebraked and illustrated with the brake units 10 comprising theservice/emergency units 11 and the booster units 12. For this purposethe fluid under pressure includes a fluid pressure source comprising thevehicle compressor 50 arranged in a serial fashion with first and secondtank means. The first tank means may be considered as comprising the wettank 51 and the dry tank 52 connected by a suitable conduit between thecompressor 50 in serial fashion. The fluid pressure source furtherincludes an emergency tank 53 mounted to be supplied from the dry tank52 and suitably connected thereto. The emergency tank 53 is connected tothe dry tank 52 by a conduit including a oneway check valve 54 whichprevents the loss of the fluid under pressure or the fluid flow from theemergency tank 53 to the dry tank 52 when the fluid in the dry tank 52is exhausted. To operate the braking units 10 as service brakes, theyare connected to the dry tank 52 of the first tank means by means of afluid conduit 55 connected between the tank 52 and a treadle valve 56.The output end of the treadle valve 56 is connected to the exhaust valve57 by means of suitable service conduits 58. In the same fashion theexhaust ports of the exhaust valve 57 are connected by suitable conduits58 to the service ports 34 of the service/emergency units 11.

The booster unit 12 as well as the emergency portions of theservice/emergency units 11 are operated from the emergency tank 53. Forthis purpose the fluid conduit '60 is connected to the emergency tank 53in parallel with a booster brake control 61 and a commercially availablemodulated emergency valve 62. The booster brake control 61 has itsoutput port connected by means of a booster conduit 63 to a quickrelease valve 64. The quick release valve 64 is coupled by means of apair of output ports in parallel relationship to the booster ports 40for the booster units 12 by means of the fluid conducts 65. The outputport of the emergency valve 62, in turn, is connected by means of theemergency conduit 66 to the exhaust valve 67. The exhaust ports of theexhaust valve 67 are connected to the emergency conduit 68 to theemergency ports 41 of the service/emergency units 11.

With the above construction in mind, it should now be appreciated thatthe operation of the serviceportion of the service/emergency units 11 isconventional. The service units, and in particular the service diaphragm33, may be actuated by the vehicle operator through the manual operationof the treadle valve 56 to thereby admit the fully pressurized fluid tothe fluid chambers S for actuating the diaphragms 33 thereby causing themovement of the rods 13 and thereby the immediate and full applicationof the service brakes. In the same general fashion, the booster brakes12 are operated by the operation of the booster brake control 61. Inthis instance, however, the pressurized fluid is exhausted from thechambers 22 of the booster units 12 to release the comprlelssion springs16 and thereby actuating the brakes In addition to these controldevices, the operator can control the pressurization of the fluidapplied to the chamber E of the emergency service units 11 through theoperation of the emergency valve 62. It should be appreciated that theoperation of the emergency valve 62 controls the pressurization of thechamber E and thereby the increment of movement of the brake operatingrod 13 in response to the movement of the emergency diaphragm 35 inaccordance with the judgment of the operator as to the required amountof braking. The pres surization is eifected by the movement of the valve62 by the motor vehicle operator to increase or decrease thepressurization of the fluid chamber E.

' Now referring to FIG. 10, another fluid control system is describedincluding a further safety feature and embodying the present invention.The fluid control system illustrated in FIG. 10 is the same general typedisclosed in FIG. 9 except that the -booster unit 12 is arranged in afluid control system with a diflerential pressure check valve 70arranged downstream from the control valve or parking valve 61 to affordfurther protection to the vehicle operator. A particular fluid controlsystem and components thereof is more fully described in theaforementioned copending application bearing Ser. No. 467,189; now Pat.No. 3,285,672. It should be appreciated that with the aforementionedmodification of the fluid control system, the system of FIG. 10 operatesin the same general fashion as the system of FIG. 9.

It should now be appreciated that the present invention has advanced thestate of the art through the provision of an improved braking devicecapable of use as a power actuated service brake and as an operatorcontrolled, power activated emergency brake wherein the brake may beactuatued in controlled increments in accordance with the judgment ofthe vehicle operator.

We claim:

1. In a vehicle braking system of the type employing separate brakingassemblies for each of a plurality of wheels, each adapted to beactivated to braking position by a fluid operated brake actuatorcomprising a source of fluid under pressure comprising a compressorserially connected to a pair of tank means for supplying fluid underpressure to a vehicle braking system and including a one-way check valveconnected between said tanks to maintain the fluid under pressure in thedownstream tank when the upstream tank is exhausted thereby maintainingthe tank as an emergency tank, a fluid operated brake actuator for eachof said plurality of wheels characterized in that each brake actuator isalternately operative as a service brake and as an emergency brake andhaving individual fluid ports for operating the brake actuator as aservice brake or an emergency brake, a first exhaust valve meansconnected to the emergency fluid port of the brake actuator, a controlvalve means connected between said emergency tank and said exhaust valvefor controlling the pressurization of the brake actuator functioning asan emergency brake in controllable increments, a second exhaust valvemeans connected to the service brake port of the brake actuator, controlvalve means connected between said second exhaust valve means and saidupstream tank for placing the brake actuator in either a fully actuatedposition or fully deactuated position, mechanically powered alternatebrake setting means effective to set the vehicle brakes upon failure ofpressurized fluid, said mechanically powered brake setting meansincluding means for holding said brake setting means deactivatednormally by use of pressurized fluid, manually controlled valve meanssonnected to said emergency tank to receive fluid under pressure readilyaccessible to the vehicle driver from his normal driving position tovent pressurized fluid from said mechanically to set and hold themechanically powered brakes positively set until pressurized fluid isagain admitted to said mechanically powered brake setting means, andpressure diiferential responsive check valve means in the pressurizedfluid supply to said means for holding the brake setting meansdeactivated, said pressure differential responsive check valve beingpositioned downstream from said manually controlled valve whereby theopening of said check valve to vent fluid to the atmosphere causes anabrupt pressure drop on the downstream side of said manual valve, saidcheck valve means including means operable to pass pressurized fluid tosaid holding means and to hold such fluid captive against reverse flowuntil the system pressure falls below a predetermined minimum operatingpressure whereupon said captive fluid is automatically vented to theatmosphere thereby allowing said mechanically powered brake settingmeans to set the vehicle brakes, and pressure responsive meansoperatively connected with said manual valve operable by said abruptpressure drop to close said manual valve to prevent fluid loss from thebraking system as a whole.

2. In a vehicle braking system as defined in claim 1 wherein said brakeactuator comprises a housing having first and second flexible diaphragmssupported therein and References Cited UNITED STATES PATENTS 3,003,82510/ 1961 Kemble.

3,285,672 11/1966 Avrea 303-9 3,326,090 6/ 1967 Cruse 9264 3,385,6365/1968 Cruse 91-4l1 FERGUS S. MIDDLETON, Primary Examiner J. J.McLAUGI-ILIN, JR., Assistant Examiner US. Cl. X.R.

